Of interest, U.S. Pat. No. 5,516,580, issued May 14, 1996 to Frenette et al., assignors to Groupe Laperriere et Verreault Inc. and Cascades Inc., describes an insulating material of loose fill short cellulose fibers and longer bonding synthetic fibers, and also an outer sheath that is heat-fused with outer sheaths of other synthetic fibers, forming a matrix that has pockets to retain the loose fill cellulose fibers. The insulating material is described as useful for both thermal and acoustical applications.
Additionally of interest are U.S. Pat. No. 5,362,539, issued Nov. 8, 1994 to Hall et al., assignors to Owens-Corning Fiberglas Technology, and U.S. Pat. No. 6,345,688, issued Feb. 12, 2002 to Veen et al., assignors to Johnson Controls Technology.
The '539 patent describes an insulation assembly that has a mineral fiber core and a polymer film positioned adjacent the surfaces of the core. The film is attached to at least one of the side surfaces of the core and has several openings adjacent at least one of the side surfaces.
The '688 patent describes a tunable sound absorber including a fibrous batt that has coupled to its surface a film, where the fibers penetrate the film to create perforations. The perforations transfer sound energy to the batt and the sound energy is absorbed by the batt. The '688 patent teaches that the porosity, i.e., the frequency of the perforations, as well as their diameter and depth, are the means by which surface resistance can be varied in order to alter acoustical absorption characteristics of sound absorbers as surface resistance creates drag on sound energy as it passes through the perforations. In particular, the '688 patent describes a surface porosity of about 400,000 perforations per square meter as a desirable level of surface resistance to attenuate a wide range of sound frequencies.
Also of interest are U.S. Pat. No. 5,023,131, issued Jun. 11, 1991 to Kwok, assignor to du Pont de Nemours, and U.S. Pat. No. 5,057,168, issued Oct. 15, 1991 to Muncrief, assignor to Greenwood Cotton Insulation Products. Each of these patents describes a batt. The former describes a batt of 75–85 weight % cotton fibers and 15–25 weight % copolyester binder having a melting point from 230–340° F., where the preferred copolyester is terephthalate/isophthalate copolyester. The latter describes a particular process to make a batt of natural fiber, such as cotton, and synthetic binder fiber, such as polyester.
Of background interest is U.S. Pat. No. 4,509,304, issued Apr. 9, 1985 to Epes. This patent describes a device for installing batts of insulation into preexisting structures.
With respect to scrim, of background interest are U.S. Pat. No. 5,994,242, issued Nov. 30, 1999 to Arthurs, assignor to Intertape Polymer Group, and U.S. Pat. No. 5,139,841, issued Aug. 18, 1992 to Makoui et al., assignors to James River Corporation. The former describes a woven scrim layer formed from a thermoplastic polymer having a coating on at least one side of an elastomeric polymer, such as a coating of an ethylene/butene copolymer sold under the trademark FLEXOMER® by Union Carbide. The latter describes a disposable towel of superior wet strength and water absorbency having a scrim coated with a superabsorbent hydrophilic polymer, with a nonwoven fibrous cellulosic web bonded to the coated scrim.
The contents of all patents are hereby incorporated by reference.
Generally, the ability of an acoustical absorber to absorb sound increases with mass. Separation within the material without undue increase of mass (i.e., decreased density) further improves acoustical efficiencies. In addition to having good sound absorption efficiencies, acoustical absorbers should also be as light as possible so as not to contribute substantially to the overall weight of the structure with which the absorber is used. Particularly for automotive vehicles, the absorber should also completely fill the voids and spaces in the vehicle body. Any gaps between the absorber and the automotive body or neighboring absorber material reduces sound absorption. To improve fit and reduce gaps, automotive manufacturers must custom-make, or the user must cut, the absorber to fit the voids and spaces. Of course, this increases the cost and time required to provide the vehicle with the absorber material. An alternative is to make absorbers from compressible material and force the material into the voids and spaces. After compression, the absorber decompresses toward its original volume and fills the voids.
Acoustical absorbers are made from various types of sound absorbing materials, for instance, polyurethane foam which has been molded or die cut to make a rigid form that conforms to the structure with which the absorber is used, such as an automotive vehicle body. Alternatively, the liquid components of the urethane foam can be poured directly into the automotive body and hardened in place into rigid polyurethane. However, not only is acoustical foam expensive, but also the pouring process can produce toxic gasses and therefore requires both that the air is ventilated and that the workers wear protective clothing. Occasionally, the foam will fail to fill the void completely and the defective product will need to be reworked.
Fibrous materials also find use as acoustical absorbers, including use in automotive vehicles. The fibrous materials may include cellulose, glass, polyethylene, polyester, and polypropylene. The fibers are mechanically or chemically bound to form a blanket or batt, often using conventional textile processing techniques.
Drawbacks are inherent in many of the conventional fibrous batt products. Typically, they are heavy, dense, or expensive materials and thus add greatly to the weight or cost of the structure, which is particularly a detriment for automotive vehicles. Some fibrous products are not flexible enough to conform to the abnormal spaces or voids into which they are installed. Also, some fibrous products are hard to install because they are difficult to compress to accommodate small openings and often lack the ability to recover well from compression when installed into a void. Moreover, some of the fibrous materials, particularly fiberglass, present environmental and handling concerns. Additionally, some fibrous products, particularly cotton, easily pick up dust and dirt during handling, so it is desirous to cover them with some kind of plastic, but then they can lose flexibility and/compressibility.
For the foregoing reasons, a need exists for an improved, acoustical absorber. Ideally the absorber should show good absorption of low and high frequency sounds as well as being flexible in order to conform to abnormal voids and spaces in structures, such as buildings and motor vehicle bodies. The absorber should be compressible and then recover quickly from compression, be easy to install quickly in an assembly line, and be environmentally safe and economical to produce.